SUMY, Ukraine — During more than three years of Russia's full-scale war on Ukraine, the front line has also served as a kind of vicious, real-time classroom.
Both Ukraine and Russia have made, and learned from, mistakes. So, too, has North Korea — which last fall sent 11,000 elite soldiers to support Russia's military in the Russian region of Kursk, where Ukrainians had made a surprise incursion last summer.
North Korean troops' progress — especially in drone warfare — has potential implications not only for Russia's war on Ukraine but also peace on the Korean Peninsula.
Across the border from Kursk, in Ukraine's northeastern Sumy region, Ukrainian soldiers who battled those soldiers described how the North Koreans went from suffering massive losses to learning electronic warfare.
"They went from using World War II tactics to managing on the battlefield with drones," Capt. Oleh Shyriaiev, commander of the 225th Separate Assault Brigade, told NPR. "And they learned very quickly."
Russia has now regained control of nearly all of Kursk. As ceasefire efforts stall, Ukraine's defense intelligence has already warned that Russia could deploy North Korean soldiers in a new ground offensive this summer. Ukrainian President Volodymyr Zelenskyy told reporters that Russia is amassing 50,000 troops along the border with Sumy. The region's governor Oleh Hryhorov said Russia has already captured several Ukrainian villages along the border.
Andriy Chernyak, a spokesman for Ukraine's defense intelligence, told NPR that North Korea has the reserves to send up to 150,000 additional troops to fight with the Russians against Ukraine.
That also worries South Korea. If the Ukraine war continues and North Korea commits more troops, their battleground knowledge could pose a threat to South Korea, says Cha Du Hyeogn, a former intelligence adviser to the South Korean government who is vice president of the Asan Institute for Policy Studies in Seoul.
"The more North Korean soldiers are trained in drone warfare, the more the risk rises that they could use these war skills in Korea," he says.
South Korea was caught off-guard in 2022, when five North Korean drones entered South Korean airspace without being detected.
Ukraine's military intelligence chief, Kyrylo Budanov, told The War Zone publication on June 10 that Russia has agreed to supply technology and know-how to the North Koreans on how to build long-range Shahed-style drones and improve the accuracy of short-range ballistic missiles.
Early deployments
In Sumy earlier this year, several Ukrainian soldiers who fought North Korean soldiers in Kursk spoke with NPR about their experiences. At the request of Ukraine's military, NPR is identifying the soldiers and non-commissioned officers interviewed for this story by their first name or military call sign for security reasons.
We met Vlad, a 31-year-old soldier in Ukraine's 8th special operations regiment, at a diner in Sumy, where he was on a break from the front line. He recalled first hearing last fall that North Koreans would be fighting in Kursk. In December, he spotted an unusually large formation of enemy soldiers in drone footage. He said he was sure the soldiers weren't Russian, "just by their behavior on the battlefield, by how differently they move, their general tactics."
He noticed that despite the group's size — "20, 30 soldiers" — the troops moved together, even in open fields, where they could be spotted by drones. Vlad said the soldiers appeared fit, fast and quick to maneuver.
"So it is a much more disciplined way of fighting that we observed from Russians," Vlad said.
Moving in such groups in open fields, however, left these soldiers exposed and easily spotted by drones. Vlad also noticed that the North Koreans risked their lives to retrieve the bodies of their colleagues from those fields.
"I've never seen the Russians do that," Vlad said.
Easy targets — at first
Andriy, 26, who commands an air surveillance unit in the 61st brigade, said he also noticed the North Korean soldiers appeared unfazed by drones early in their deployments to Kursk.
He mentioned a Ukrainian bomber drone nicknamed "Baba Yaga," after a supernatural witch. He said Russian soldiers are terrified of this drone because it is larger and louder than other drones.
"When Baba Yaga flies over the Russian units, it gets to them," he said. "It sounds like a helicopter is flying over you."
Russian units would scatter immediately, but "the North Koreans simply continued carrying out their task without paying heed," Andriy said. "They would go straight ahead, without any cover, straight through the field. They wouldn't even hide if there was artillery fire somewhere close by. They wouldn't hide from our FPV [first-person view] drones."
Ukraine has pioneered the use of FPV drones to track and attack Russian and North Korean soldiers.
Because the North Koreans moved in big groups at first, Andriy said they were easy targets for artillery, "and if some of them survived, it was easier for FPV drones to find them."
Volodymyr, 35, who leads a reconnaissance unit in the 61st brigade, noticed that at night, the soldiers wrapped themselves in Mylar ponchos, also known as space blankets, to avoid being detected by the Ukrainian thermal imaging.
"Maybe they used these incorrectly, maybe it was a defective batch, but when they put these on, they were visible from afar," Volodymyr said.
"Early on the Russians treated the North Koreans like cannon fodder," he said. "If North Koreans died, then fewer Russians would be killed."
He said his unit tried to capture one injured North Korean soldier who got separated from his group and hid out in abandoned homes.
"We couldn't catch him because he was young and in really good physical shape," Volodymyr said. "He managed to scale a fence, and our 50-year-old soldiers tried to follow, but by the time they climbed down, he was gone."
The soldiers spotted him later, running with his backpack and equipment, even though he was injured. When the soldier realized he was cornered and noticed the Ukrainian troops closing in, Volodymyr said, the soldier pulled out a grenade and blew himself up.
"We hoped he would survive"
For weeks over the winter early this year, Ukraine's military tried to capture a North Korean soldier in order to prove to Western allies that Pyongyang had joined the fight against Ukraine.
It wasn't easy. Ukrainian soldiers told NPR it seemed clear that the North Koreans would rather die than become prisoners of war.
Cha, the Seoul-based security analyst, says they make this choice out of concern for their families back home. Pyongyang views captured soldiers as traitors.
"Their relatives and families often suffer the consequences and are treated badly in North Korean society," he explains.
Soldiers from Ukraine's 8th regiment captured one wounded North Korean soldier early this year. The soldier had been badly injured in a shootout in Kursk with a Ukrainian fighter from the 8th regiment whose call sign is Bulat.
"Our medic immediately provided him with help and bandaged his leg and arm," Bulat said. "The soldier also has a shrapnel wound to his cheek. Our medic bandaged that too."
The North Korean had already lost a lot of blood and was in serious condition, floating in and out of consciousness, Bulat said.
"Our medic did what he could," Bulat said. "And then we continued to fight. We hoped he would survive. He died on the way to the stabilization point."
In early January, Ukraine's special forces captured two North Korean soldiers in Kursk. The soldiers, 21-year-old Paek and 26-year-old Ri, remain in Ukrainian captivity. Zelenskyy posted videos of Ukrainian authorities questioning the two. Ukrainian and independent Russian media reported that one of the soldiers had an ID issued in the name of a Russian citizen from southern Siberia.
In interviews with the Wall Street Journal, published in February, the North Koreans said they didn't know they were being sent to Russia until they arrived. Once there, they told the paper they underwent military drills that included drone training.
Some 4,700 North Korean soldiers were killed fighting in Kursk, according to South Korea's spy agency, with most dying early in their deployments.
Diaries, drones … and progress
Ukrainian soldiers collected the belongings of some North Korean soldiers killed in battle. They included Russian military ID cards, where names were written in Russian but signed by the soldiers in Korean, as well as outdated cell phones, SIM cards and first-aid instructions issued by Russia but written in Korean.
There were also notebooks, which NPR has viewed and confirmed as authentic, that served as diaries. One included handwritten passages from a speech that North Korean leader Kim Jong Un delivered to military officers last November and a "monthly life review" by one soldier that included a confession of stealing Russian goods after being "captivated" by them. Also in the diaries: instructions on how to stay out of artillery fire and how to spot and destroy drones. "One person among three lure it out," one soldier wrote. "The drone stops when the person stops, so the other two destroy it with an aimed shot."
Maksym, a Ukrainian drone operator, said the North Koreans seemed to take such instructions to heart. He noticed how they calmly stood in fields and shot at drones with rifles "very precisely."
"They shot down my drones multiple times," Maksym said.
After Kursk
By March, Russian and North Korean soldiers had pushed Ukrainian troops out of most of Kursk, said Shyriarev, the Ukrainian commander. He said his own soldiers adapted their battlefield strategy.
"We instructed our soldiers to avoid direct battles with North Korean troops," he said. "We planted mines, and our plan was that if they started an assault, they might fall into our traps."
At the time, Moscow and Pyongyang had still not confirmed North Koreans were even in Kursk. Zelenskyy had spent months offering warnings about North Korea supplying Russia with both weapons and soldiers.
"The world does almost nothing to counter the criminal collaboration between Russia and North Korea," he said in his evening video address on December 23.
It wasn't until spring that Russia and North Korea both publicly acknowledged the soldiers.
In late April, the Russian army's chief of staff, Gen. Valery Gerasimov, declared that Russia had pushed Ukrainian soldiers out of nearly all of Kursk, hailing the "fortitude and heroism" of North Korean soldiers. Pyongyang also confirmed the North Korean troops were there, with an official statement praising their "heroic feats." Putin followed suit. Several North Korean soldiers were even on Red Square for Russia's Victory Day celebrations on May 9, shaking hands with the Kremlin leader.
"We will always honor the Korean heroes who gave their lives for Russia, for our common freedom, on par with their Russians brother in arms," Putin said in a statement on the Kremlin's website.
Ukraine currently controls only a fraction of Kursk. There's been no recent information on what's next for North Korean troops who fought there.
Cha Du Hyeogn, of the Asan Institute for Policy Studies, says North Korea had a rationale for joining the fight in Kursk.
"It can now claim that it is not unjustly intervening in the aggressive war by Russia but rather assisting Russia, a comrade country under invasion," he says.
He said North Korea could cite a bilateral treaty the two countries signed during Putin's visit to Pyongyang in June 2024, which includes a pact for immediate military assistance if either country faces armed aggression.
But Cha expects that Pyongyang won't agree to send its troops to Russian-occupied territory in Ukraine unless it gets something in return from the Kremlin, "potentially advanced nuclear weapons manufacturing."
"From Pyongyang's perspective, if it can obtain advanced technology and weapons systems, it may be willing to deploy troops to Ukraine, even at significant cost," he says. "However, if the compensation consists merely of energy and food supplies, North Korea would need to weigh the decision more carefully."
According to South Korea's intelligence agency, Russia is currently providing North Korea with "technical guidance for reconnaissance satellites and launch vehicles, as well as physical assets such as drones, electronic warfare equipment and SA-22 surface-to-air missile systems."
Russia is also modernizing various industries and letting in North Korean laborers who can't work abroad because of sanctions.
In Ukraine, Budanov, the military intelligence chief, warned in an interview with The War Zone that these North Korean laborers could be enticed into signing contracts with the Russian military.
"And it wouldn't be the warriors from North Korea," he said. "It would be Russian warriors but of North Korean nationality."
Capt. Oleh Shyriarev, who fought the North Koreans in Kursk, said Russia would not have been able to recapture its territory without the North Koreans. Shyriarev said the soldiers learned on the front line how to fight a modern war.
"That," he says, "is a fact."
Tetiana Burianova and Polina Lytvynova contributed reporting from Sumy. NPR's Se Eun Gong and Anthony Kuhn contributed reporting from Seoul and Charles Maynes from Moscow.
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